CO₂ electroreduction into valuable products holds great promise for energy supply and environmental remediation but remains a challenge due to the lack of high-performance electrocatalysts. Herein, we developed an efficient strategy to prepare highly active Fe single-atom catalysts (Fe–N₅/Fe–N₆) by tuning the coordination number of Fe with N towards CO₂ electroreduction. The faradaic efficiency of CO for Fe–N₅ exceeded 90% ranging from −0.35 to −0.65 V versus the reversible hydrogen electrode (vs. RHE) towards CO₂ electroreduction. The turnover frequency of CO for Fe–N₅ reached 5006 h⁻¹ at −1.05 V vs. RHE, which was 3.8 times that (1324 h⁻¹) of Fe–N₆. Besides, CO was generated at an overpotential as low as 50 mV over Fe–N₅, smaller than that (90 mV) over Fe–N₆. Density functional theory calculations demonstrated that Fe–N₅ facilitated the adsorption and activation of CO₂ to form the *COOH intermediate, thus leading to superior selectivity and activity for CO₂ electroreduction.